Organic electroluminescent display panels (hereinafter referred to as organic EL display panels) contain an image display array comprised of a plurality of light emitting pixels arranged in intersecting rows and columns.
In addition to the image display array, organic EL display panels may also contain display regions dedicated to the display of symbols or icons, such icon display regions disposed on a common support in a selected region adjacent to the image display array.
Tang et al., U.S. Pat. No. 5,294,870 disclose an organic EL multicolor image display device. For purposes of clarity, the multicolor aspect of the Tang et al. device will not be further discussed. In the construction of the Tang et al. device it has been found advantageous (see particularly FIG. 2) to provide a series of parallel walls 107 over a surface on a support, and extending orthogonally across a series of parallel first electrodes disposed on the support. Each single wall separates one set of pixels from an adjacent set of pixels. Each wall has substantially vertical side surfaces and a top surface extending in a direction parallel to the support. Each wall serves as an integral deposition mask for forming second electrodes (A, B, and C in FIG. 2) by line-of-sight vapor deposition of an electrode material under an angle relative to the substantially vertical side surfaces of the walls.
Nagayama et al., European Patent Application 0 732868 A1 discloses an organic EL display panel having electrical insulation ramparts 7. Each rampart has an overhanging portion 7a, with various rampart cross sectional views shown in FIGS. 7A-7H of the Nagayama et al. disclosure. Each of these single ramparts separates one set of light emitting portions (or light emitting pixels) from an adjacent set of light emitting portions. Each of the single ramparts serves as an integral deposition mask for forming second display electrodes 9 over an organic function layer 8 disposed over a portion of first display electrodes 3.
The walls of the Tang et al. device, and the ramparts of the Nagayama et al. device, are constructed on a device surface from an electrically insulative material which is patterned by a photolithographic process well known in the art. The process is selected to remove the insulative material from areas extending between neighboring walls or ramparts, leaving behind on the device surface a patterned layer which constitutes the walls or the ramparts.
It has been found that particle residue can become lodged at the base of the walls or against the side of the walls constructed in accordance with the teachings of Tang et al. in the aforementioned U.S. patent, during or subsequent to the wall patterning process. It is anticipated that particle residue can become lodged under the overhanging portions of the Nagayama et al. ramparts. The problem of particle residue can be more readily appreciated from a schematic perspective view shown in FIG. 1A, and from a schematic cross sectional view of FIG. 1B, in which only four walls are depicted for clarity.
In FIG. 1A, three anode electrodes A1-A3 are disposed on a support 12. Four walls W1-W4 of insulative material are shown disposed over the anode electrodes and on the support therebetween, and are positioned orthogonally to the anode electrodes.
A particle defect D is schematically indicated as being lodged against the anode electrode A1 and against an upper edge of the wall W2, respectively.
FIG. 1B is a schematic cross sectional view taken along the line 1B--1B in FIG. 1A, depicts an additional layer of an EL medium 14 overlying the anode electrode A1 and the upper surfaces of the walls. The particle defect D is lodged against the anode electrode A1 and extends to an upper surface of the wall W2. Further indicated are cathode electrodes C1-C4 comprised of a metallic cathode electrode material which has been vapor deposited under a deposition angle .THETA. with respect to the side surfaces of the walls whereby the walls serve as an integral mask for selective deposition of laterally separated cathode electrodes, i.e. separated in the absence of the particle defect D.
The particle D causes a deposited organic EL medium layer 14 to extend from the right side of the wall W1 along the anode electrode A1, along and over the defect D, and over the top surface of the wall W2. More importantly, the cathode electrode C1 is connected to the adjacent cathode electrode C2 due to vapor deposition of the electrode material over the EL medium layer in the region overlying the defect D. Effectively, the electrical connection between cathode electrodes C1 and C2 at the defect position causes light emission from pixels P located at the intersection areas between any anode electrode and either cathode electrode C1 or C2 when an electrical potential difference is applied between any anode electrode and either cathode electrode C1 or C2.
By comparison, the defect-free walls W3 and W4 have an associated EL medium layer and associated cathode electrodes C3 and C4 clearly laterally separated from one another.
The problem of light emission from pixels located at the intersection between any anode electrode and either cathode electrode C1 or cathode electrode C2 makes a device pixel useless.
Complete and reliable elimination of particle defects cannot be achieved in the construction of walls or ramparts.